[056/145] jbd2: fix theoretical race in jbd2__journal_restart

Submitted by Kamal Mostafa on July 17, 2013, 10:46 p.m.


Message ID 1374101277-7915-57-git-send-email-kamal@canonical.com
State New
Headers show

Commit Message

Kamal Mostafa July 17, 2013, 10:46 p.m. -stable review patch.  If anyone has any objections, please let me know.


From: Theodore Ts'o <tytso@mit.edu>

commit 39c04153fda8c32e85b51c96eb5511a326ad7609 upstream.

Once we decrement transaction->t_updates, if this is the last handle
holding the transaction from closing, and once we release the
t_handle_lock spinlock, it's possible for the transaction to commit
and be released.  In practice with normal kernels, this probably won't
happen, since the commit happens in a separate kernel thread and it's
unlikely this could all happen within the space of a few CPU cycles.

On the other hand, with a real-time kernel, this could potentially
happen, so save the tid found in transaction->t_tid before we release
t_handle_lock.  It would require an insane configuration, such as one
where the jbd2 thread was set to a very high real-time priority,
perhaps because a high priority real-time thread is trying to read or
write to a file system.  But some people who use real-time kernels
have been known to do insane things, including controlling
laser-wielding industrial robots.  :-)

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
[ luis: backported to 3.8: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
 fs/jbd2/transaction.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Patch hide | download patch | download mbox

diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 73b9253..2f78ba3 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -500,10 +500,10 @@  int jbd2__journal_restart(handle_t *handle, int nblocks, gfp_t gfp_mask)
 	if (atomic_dec_and_test(&transaction->t_updates))
+	tid = transaction->t_tid;
 	jbd_debug(2, "restarting handle %p\n", handle);
-	tid = transaction->t_tid;
 	need_to_start = !tid_geq(journal->j_commit_request, tid);
 	if (need_to_start)